Is 800 fill power goose down better than 600 fill?

Yes, in warmth-to-weight terms. Higher fill power means each ounce of down lofts more and traps more air, so an 800 fill comforter delivers similar warmth with less bulk and weight than a 600 fill one.

Do I need a duvet cover with this comforter?

It is not required, but a cover protects the cotton shell from oils and sweat and cuts down on washing. Washing down comforters often is hard on the fill, so a cover extends its life.

Will it be too warm for summer?

For many sleepers, yes. An 800 fill comforter is a solid choice for cool rooms and cold months; in warm bedrooms, most people use a lighter blanket instead.

Is it good for people with allergies?

Goose down can trigger reactions in people sensitive to feathers or dust mites. If you react to down, a down-alternative comforter is the safer pick.

How should I clean it?

Use a duvet cover day to day and wash rarely. When you do wash it, use a front-loading machine on a gentle cycle with down-safe detergent, then tumble dry low with dryer balls until fully dry.